The present invention relates to a mass spectrometer and a method of mass spectrometry. In some embodiments, the invention relates to a hardware module and method for acquiring and compressing mass spectral data, for example for onward analysis.
Mass spectral data is typically generated by the impact of ions on one to provide information as to the mass to charge (m/z) ratios and or more ion detectors, which provide signals which can be processed the number of ions (e.g. by the intensity of the ion count) at a particular m/z, the information typically being provided in the form of a mass spectrum. Mass spectra may be further analysed to elucidate structural information about the compounds analysed.
Modern mass spectrometers are capable of acquiring very large quantities of data as a result of both their sensitivities and the number of different forms of analysis they are able to perform on a single sample. For example, where, say, a tandem mass spectrometer such as a quadrupole time-of-flight mass spectrometer is coupled to a liquid chromatograph, the instrument may be capable of acquiring several thousand individual mass spectra for a single sample. These spectra result from the time-of-flight mass analyser obtaining up to several thousand spectra per second which may correspond to many m/z settings of the quadrupole mass analyser in turn from an array of residence times in the column of the liquid chromatograph. Where an ion mobility spectrometer is also coupled to a system, for example between the liquid chromatograph and, say, a time-of-flight mass analyser, the number of spectra acquired increases again by virtue of the array of ion drift times which may be analysed in the mass analysers.
Furthermore, where the resolution of the mass analyser(s) is very fine, a correspondingly large number of m/z and intensity data require processing and storage.
In a typical mass spectrometer, such data is transferred to computer for processing. Indeed, it is typical for the data to be transferred to and through a series of computers, at least one of which may be within the instrument itself, where it may be subject to optional noise-reduction algorithms where periodic background noise is effectively filtered out from the mass spectral data as described in British patent application GB2409568. It is typical to store the data in one or more databases in one or more of the computers such that it can be searched and retrieved by users at a later date.
FIG. 1a shows a spectrometer system of the prior art e.g as disclosed in WO2010136775 which is also incorporated here by reference, the system having an ion source 1, an acceleration region 2, a field-free region 3, a reflectron (ion mirror) 4, a detector 5, an acquisition system 6, an embedded computer system 7 and a host computer system 8.
Ions formed in the ion source from the sample compound enter the acceleration region where they are driven by an acceleration voltage pulse into the field-free region. The ions are accelerated to a velocity determined by the energy imparted by the acceleration pulse and their mass, lighter ions achieving a higher velocity.
A reflectron is used to increase the length of the path the ions take from the acceleration region to the detector for a given length of analyser housing. This allows greater separation in time between ions with different velocities.
Ions arrive at the detector after a time determined by their velocity and the distance traveled, thus enabling their mass to be determined.
The output of the detector is sampled by the acquisition system which then generates a mass spectrum that is passed to the embedded computer system. The operation of the acquisition system is described in greater detail below.
The embedded computer system passes the mass spectrum data to the host computer system for further analysis and storage. The embedded computer system can also analyse the data for data dependent acquisitions. This allows the content of the mass spectrum data to be used to change the mass spectrometer's configuration on a scan-by-scan basis.
FIG. 1b shows a block diagram of the acquisition system of the prior art comprising, an acquisition engine 9, a data throughput optimization module 19 and an Ethernet interface 11 for the output of data to the embedded computer system 7. The data throughput optimization block itself comprises a data compression engine 21, a ring buffer 13 and a hardware protocol stack 15.
The detector signal from the mass spectrometer that is input to the acquisition system is first sampled by a high speed analogue-to-digital converter (ADC) within the acquisition engine. The acquisition engine then detects any peaks present within the signal and converts them useable information e.g. comprising of time and intensity.
The next stage of the optimization block is the data compression engine 21 that uses an LZRW3 (Lempel-Ziv Ross Williams) compression algorithm to provide data compression on the data from the data acquisition engine.
The output of the data compression engine is input into the ring buffer 13, whereby the ring buffer 13 formats the data and transmits it to a hardware protocol stack, which in turn transmits the data to a computer system for processing.
As the quantity of data that is collected increases, the speed of transfer of that data between devices and the speed of processing that data into usable forms is compromised. This represents a particular problem where data cannot be transferred and recorded onto a computer storage medium as fast as the mass spectrometer is able to acquire it. In such instances, data may be lost on an indiscriminate basis. Further problems arise in providing sufficient data storage space and in the processing power required for the one or more computers to provide the data in a usable and interpretable form.
The present invention seeks to address these problems by providing a hardware module and a method for compressing mass spectral data to increase the speed at which such data can be processed and transferred.